Naturally occurring petroleum may be made up of a variety of different hydrocarbon substances. These may include paraffinic, isoparaffinic, cycloparaffinic and aromatic hydrocarbons, and may range from light gases to kerosene to heavy asphalts.
Linear paraffins from petroleum are often used in forming detergents or surfactants. Linear paraffins, typically in the C10 to C24 range, may be alkylated with benzene directly or after undergoing dehydrogenation to form alkylbenzene, which is then sulfonated to form alkylbenzene sulfonate detergents. Because petroleum-derived paraffins may be highly branched, having one or more branches of different lengths that may be randomly positioned along the main carbon chain, it is difficult to isolate linear paraffins from the mixture to achieve high linear purity. Additionally, branched-chain alkylbenzene sulfonates, while providing good detergency or surfactancy, are not easily biodegraded. Because of increasing environmental concerns, there has been an emphasis on producing high purity linear alkylbenzene (LAB) feedstock for use in making linear alkylbenzene sulfonate (LAS), which is readily biodegraded.
In the manufacture of LAS, linear purities for the paraffin feedstock may be as much as 95% and even 98% or more by weight of the paraffin feedstock. Petroleum derived hydrotreated distillates containing the appropriate carbon number hydrocarbons or paraffins typically only have a linear content of from 40% or lower by weight. Thus, procedures for purifying linear paraffins are needed. Because conventional hydrotreated distillates usually include relatively large amounts of various cyclic or branched paraffin components, separating the linear paraffins from non-linear paraffins is impossible using distillation separation techniques. This is due to the large degree of overlap in the boiling points of the non-linear paraffin components with those of the linear paraffins. Therefore, separation of the linear paraffins is usually carried out using shape-selective molecular sieve separation. Molecular sieve separation is quite involved and requires the use of costly molecular sieve adsorbents and equipment. Separation of linear paraffins from non-linear paraffins using urea adduction techniques have also been employed, but are less efficient and are not widely practiced commercially.